Switch overload

ABSTRACT

An overload switch having a core associated with a permanent magnet with two sets of limbs and armatures associated with each set connected by a lever. The sets of limbs are provided with windings which are wound so that a current in the windings increases the magnetic attraction in the case of one armature, but decreases it in the case of the other armature. At a predetermined current level, a spring pivots the lever to release a catch to open the switch.

Int Cl Foreign Application Priority Data Field of Search References Cited UNITED STATES PATENTS 6/ 1922 Lucas ..335/232 Unlted States Patent 1151 3,675,167

Ellenberger July 4, 1972 541 SWITCH OVERLOAD 1,645,019 10/1927 Oppennan .335 16 1 847 339 3/1932 Freeman .335/232 72 1 1 11 b Ell e v l 1 fi ,522? Atdmf 2,120,037 6/1938 OHagan ...335/236 2,941,130 6/1960 Fischer et 61.. ...335/230 Assigneel Ellenberger & Poenssen Gmbll, Altdorf 3,278,873 10/1966 Hilgert .335/230 near Nuernberg, Germany [22] Filed: N0v 21970 Primary Examiner-Harold Broome AttorneyHarness, Dickey & Pierce 21 Appl.No.: 85,845

[57] ABSTRACT An overload switch having a core associated with a permanent m'agnet'with two sets of limbs and armatures associated with each set connected by a lever. The sets of limbs are provided with windings which are wound so that a current in the windings increases the magnetic attraction in the case of one armature, but decreases it in the case of the other armature. At a predetermined current level, a spring pivots the lever to release a catch to open the switch. 7

17 Claims, 5 Drawing Figures Patented July 4, 1972 4 Sheets-Sheet 2 Patented July 4, 1972 4 Sheets-Sheet 5 INVENTORT 15%JZ BYI Wfi Patented July 4, 1972 3,675,167

4 Sheets-Sheet 4 Fig.4 1.7

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swrrcrr OVERLOAD BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to overload switches of the type which have a core with a pre-established flux, e.g., by association with a permanent magnet, to retain an armature for the magnet in an attracted position, and further having a coil for producing a flux in response to a current through the coil which opposes the flux of the permanent magnet so that the magnet armature can be lified off the magnetic core by an associated spring to move a contact carrier to an ofl' position. One switch of this kind has a magnetic core with-consists of two T-shaped elements, the transverse limbs of which extend parallel to each other and the central vertically projecting limbs of which extend towards each other in spaced relationship and are provided with a coil or winding. In the event of an overload, the magnet flux provided by the coil opposes the magnetic flux of the permanent magnet so as to bend an armature to displace a contact bridge connected with the armature to an off position. A relatively small current is needed to operate the switch, but the current required is still too great for certain applications, for example, the protection of electronic elements or multiple metering instruments against excess current.

According to the present invention an overload switch is provided which includes a magnetic core comprising two sets of substantially parallel limbs with each set having at least one limb, means to pre-magnetize the limbs, a magnetic armature associated with each set of limbs, a lever associated with a movable contact carrying member connected to the armatures, a spring associated with the lever, a second contact, and including at least one winding on each set of limbs to provide a magnetic flux in response to current flowing in the windings opposing the pre-established flux in one of the sets of limbs which further is in the samedirection as the pre-magnetization flux in the other set of limbs. The armatures are magnetically held against the limbs adjacent the ends thereof against the action of the spring when the limbs are pro-magnetized and the contact carrying member. is in a contact closed position abutting the second contact so that a power input above a given value in the windings allows the armature associated with the one set of limbs to be urged away from the one set of limbs by the spring to pivot the lever and cause the contact carrying member to be released from the contact closed positron.

Preferably there are two limbs to each set with the limbs of each set having opposite magnetic poles at their adjacent ends when pre-magnetized. Also, the magnetic core is substantially saturated when pre-magnetized. The pre-magnetizing means may be a permanent magnet.

Due to the magnetic flux provided by pre-magnetizing the core, the two armatures are retained in abutment against the magnetic core limbs. As soon as an overload occurs, the permanent magnetic flux is partially ofiset in one of the sets'of limbs by the magnetic flux due to the coils, and is not greatly strengthened in the other set of limbs, since magnetic material of low saturation is used and the device is operated in the area of the kinks" in the magnetization curve, i.e., the area in which the magnetization curve merges into saturation. In this way, the holding force for one of the magnets armatures is weakened to release the one armature. Consequently, the lever connecting the armatures is pivoted by the associated spring, whereby the other armature is lifted away from its associated limbs of the magnetic core to release the contact carrier from its contact closed position.

The lever may be pivotally mounted on a displaceable slide member which is urged by the spring to move the lever and the armatures thereon away from the magnetic core. A catch member for the contact carrying member may be provided which is pivotable in the housing of the switch and connected to the slide member so as to rotate upon longitudinal movement of the slide member. Advantageously, the catch member has a cranked slot, and the contact carrying member has a projection movable in the cranked slot and in a second slot in a support in the housing of the switch when a portion of the cranked slot is aligned with the second slot, the projection being restrained agaimt sliding by rotation of the catch member and consequent movement of the slide member when the projection is in a locking position in the slots. The contact carrying member is rotatable when the projection is locked in the contact closed position. A pivotable catch may be provided which is connected to the slide member and is able to retain the contact carrying member in a position wherein it can be rotated to its contact closed position. Movement of the slide member due to release-of an armature rotates the catch to release the contact closing member.

To additionally provide thermal triggering, a birnetal strip may be providedcausing a heating coil connected in the circuit of the contact carrier, which acts on the slide member to release the contact carrying member and open the switch when it bends in response to heating by the coil.

In order that the invention may be more clearly understood, the following description is given, merely by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of one form of switch according to the invention illustrated in the switched-on positron;

FIG. 2 is a section taken along the line 2-2 of FIG. 1;

FIG. 3 is the same view as that of FIG. 1 but with the switch illustrated in the switched-off position;

FIG. 4 is a perspective view of the magnet system of the overload switch shown in FIGS. 1 to 3; and

FIG. 5 is a circuit diagram illustrating the principle of the switch of FIGS. 1 to 4.

DETAILED DESCRIPTION OF THE PREFERRE EMBODIMENT As shown in FIGS. 1 to 4, the switch has a housing comprising two housing halves 1 and 2 which may be connected together by hollow rivets extending through bores 3 in the housing halves. Also for securing the halves of the housing, both housing halves have flanges 4 and 5.

A slide member 32 has a lever 54 pivotally connected to it at 43 supporting two armatures 55 which can be held against limbs 49 i.e., pole pieces, which are part of a magnetic core. The slide member is located between the limbs 49.

A contact carrier 1 I resides in the lower half of the housing and has an upwardly extending part 23 and a sideways extending part 36. A contact 12, adapted to cooperate with a fixed contact 13 on the housing, is mounted on the carrier 11.

A catch 27 is pivoted at 26 to a metal frame member 9 within the housing, and has a pin 30 engaging a transverse slot 31 in the slide member 32 so that rotation of the catch 27 causes longitudinal movement of the slide member 32, and vice versa.

The contact carrier 11 has a pivot pin 24 rigidly secured to it which is slidable and rotatable in a slot 25 in the frame 9 and in a cranked slot or recess 28 in the catch 27. The recess 28 has one part which can be aligned with the slot 25, and a downwardly extending cranked part having an inside abut ment face 29. Once the pin 24 has been slid to the ends of both the slot 25 and the recess 28, the catch 27 can be pivoted upwardly as shown; In that position, the pin 24 is restricted so that it can rotate but cannot slide. When the catch is pivoted to this position, the slide member is moved upwardly to bear the armatures 55 against the limbs 49 of the magnetic core.

A spring 34 acts on the contact carrier 11 so that when the carrier 11 is in the restricted position it rotates to urge the contacts 12 and 13 together. If the catch 27 is pivoted downwards to being the face 29 out of contact with pin 24, the spring 34 urges the carrier 11 to open the contacts. The upper part 23 of the carrier 11 may then contact an abutment 33 on frame 9, which'is above the spring 34, so that the carrier 11 pivots about this abutment to the position shown in FIG. 3.

The fixed contact 13 is secured to a connecting member 14 which is in turn connected to a flex 15 extending out of the housing as may be seen in FIG. 1.

A switch operating pushbutton 6, shown in the switch-on position in FIG. 1, is mounted for displacement with respect to the housing and has an angular position 7 with a limb 8 guided for displacement in the metal frame 9. A spring 10 acts on the limb 8 and urges the pushbutton 6 towards its switch-off position shown in FIG. 3. In the switch-on position of FIG. 1, the limb 8 is urged against the contact carrier 11 by the spring 10.

The pushbutton has a finger 35 adapted to cooperate with a finger 37 on the part 36 of contact carrier 11. As shown in FIG. 3, these parts cooperate when the pushbutton is used to push the carrier 11 towards the position wherein it is restricted to rotational movement. The fingers prevent rotation of the carrier during this movement toward the stricted position.

A flexible conductor 17 is connected to a connecting member 16 on the housing and extends out of the housing.

A bimetal strip 18 having a vertically projecting arm 19 bearing against a conical tip of an adjusting screw 20 is secured to the connecting member 16. The bimetal strip 18 has a heating coil 21 connected at its one end to the connecting member 16 and at its other end to the bimetal strip 18. A flexible lead 22 connects the bimetal strip 18 with the upper end of the arm 23 of the contact carrier .11, and thus into the circuit having the contacts 12 and 13.

A projection 35 on the pushbutton 6 cooperates with the arm 36 of the contact carrier 11. The arm 36 is provided with a pin-shaped abutment 38 which, during the switching-on movement of the carrier 1 1 to the right, cooperates with a projection 39 on the catch 27 to pivot the catch 27 upwardly.

The slide member 32 passes through a slot 40 formed in a housing 41 of insulating material. The housing 41 is provided with a cover plate 42 of insulating material. Located within the housing 41 are a portion of the slide member 32, the lever 54, the armatures 55, portions of the limbs 49 forming the magnetic core, and portions of the windings associated with the limbs 49. A cylindrical, diametrically magnetized permanent magnet 44, which comprises the pre-magnetization means, and two semicircular yokes 45 bearing against the said magnet and the limbs 49 of the magnetic core, a plate 46 made from a non-magnetic material and a plate 47 made from a magnetic material are secured to the cover plate 42 and outside the housing by means of a hollow rivet 43. Four limbs 49 of the magnetic core which, in this case, comprise the two sets of limbs are secured, for example by welding, to four vertical bent-over portions 48. The limbs 49 bear against the plate 47 at their upper end faces and are substantially parallel to the slide member 32. The plate 47 serves as a magnetic shunt. For adjustment of the magnetic circuit, the plate 47 is adapted for rotation on the hollow rivet 43. The limbs 49 pass through slots 50 formed in the cover plate 42.

The housing 41, the cover plate 42 and the elements connected to the cover plate 42 by the hollow rivet 43 comprise a structural unit which is mounted for displacement in the axial direction in the combined housing halves l and 2 by means of screws 51 which are screwed into the plate 46 and have heads in recesses in both housing halves 1 and 2. The screws 51 carry compression springs 52. With the aid of the screws 51, the entire magnet system may be adjusted and secured with respect to the switching apparatus comprising the pushbutton 6, the slide 32, the armatures, the catch 27 etc. In this way, manufacturing tolerances may be compensated for and adjustments made.

The two-armed lever 54 which hingedly connects the two magnet armatures 55 is pivotally mounted on the slide member 32 by a pin 53. As shown in FIG. 1, the armatures bear against ground ends of a respective pair of the limbs 49 when in the switch-on position. The limbs 49 carry winding supports having windings 56. The windings 56 may be divided into continuous windings on each winding support or may be sub-divided into a plurality of individual coils. Ends 57 of the coils 56 are connected to a switchplate 58 and thus are connected with associated conducting paths 59, the connections being variable. It is possible to connect all the windings in series or to series-connect the windings 56 of one pair of limbs and to parallel-connect the two series circuits, as is shown in FIG. 4, to provide two connections 60 and 61. Furthermore, the windings may be subdivided, so that the above applies and a circuit according to FIG. 5 is produced.

An adjusting sleeve 62 is disposed in the hollow rivet 43. The adjusting sleeve 62 has an axially non-displaceable adjusting screw 63 at its upper end (FIG. 1) which is mounted in the two housing halves 1, 2 and is adapted to be actuated from outside the housing. A biased compression spring 65 bears against an annular shoulder 64 on the adjusting sleeve 62. The other end of the spring 65 contacts shoulders 66 on the slide member 32 so as to urge the armatures away from the limbs 49. The slide member 32 extends into the adjusting sleeve 62 at its upper tapered end. The slide member 32 is thus guided in the axial direction in the adjusting sleeve 62 and in the slot 40 formed in the housing 41. The compression spring 65 operates in opposition to the retaining force exerted by the magnetic flux in the armatures 55. With the aid of the adjusting screw 63, the force of the compression spring 65 may be varied within predetermined limits, thereby affecting the sensitivity of the switch, i.e., the energy input at which the contacts will open.

If the overload switch is in the switch-on position shown in FIGS. 1 and 4 wherein the two magnet armatures 55 bear against the limbs 49, the magnet armatures 55 are retained against limbs 49 by a magnetic flux 67 established by the per manent magnet. The magnitude of the permanent magnetic flux 67 (FIG. 4) determines the holding force and may be varied by rotating the plate 47. If a DC current source is connected to the connection 60, the windings 56 generate a magnetic flux 68 through the rear pair or set of limbs 49 shown in FIG. 4 in the same'direction as the permanent magnetic flux 67, while in the front pair of limbs 49 the direction of the flux 68 is opposite to the direction of the flux 67. The force holding the front magnet armature 55 is weakened in the case of a current higher than the rated current, for example 10 IN, and not greatly amplified in respect of the rear magnet armature 55 since the magnetic material has low saturation qualities, and consequently, is operating in the kink" line at which the magnetic curve merges into saturation.

On weakening of the holding force for the magnetic armature 55, e.g., for the front magnet armature according to FIG. 4, this armature is urged away from its associated limbs 49 by the compression spring 65. On rotation of the lever 54, the

rear magnet armature 55 is lifted off its associated limbs to move the slide member 32 downwardly as shown, rotating the catch 27, and therefore, allowing the contact carrying member to be urged by the spring 34 away from the contact closed position since the face 29 no longer retains the pin 24 against sliding. Thus, under the influence of the compression spring 34, the contact carrier 11 passes into the switch-off position shown in FIG. 3, in which it abuts the stop 33 of the metal frame 9 to open the contacts 12 and 13. Simultaneously, the contact carrier 11 releases the pushbutton 6, so that the latter travels, under the influence of the spring 10, to its switch-off position as shown in FIG. 3.

This triggered release of the switch occurs even though the pushbutton 6 is retained in its switch-on position as in FIG. 1, since in this position, the finger 35, is not located in the zone of movement of the finger 37 on the contact carrier 11 when the finger 37 is moving from the contact-closed position. It is not necessary to construct the switch so that the pushbutton is held in when the contacts are closed, but this feature may be a useful indication that the contacts are closed.

When the switch is in the switch-off condition as shown in FIG. 3, the contacts are closed by pressing the pushbutton 6 into the housing. When this is done, the finger 35 engages the finger 37 on the contact carrier 11, so that the carrier 11 is pushed to the right as shown. The abutment 38 on the portion 36 of the contact carrier 11 contacts the projection 39 on the catch 27 to pivot the catch anti-clockwise, to bring its face 29 into position to restrain the pin 24 of the carrier when the pin 24 moves to the end of the slot 25 and the recess 28. Pivoting of the catch 27 displaces the slide member 32 upwardly to such an extent that the magnet armatures 55 move into abutment with the limbs 49. When the pushbutton 6 is released, the spring 10 urges it at least slightly to the left as seen in FIG. 3, whereby its projection 35 disengages from the projection 37 on the contact carrier 11. The spring 34 then rotates the contact carrier 11 about its pivot pin 24 so that the contact 12 is quickly brought into abutment with the fixed contact 13. The overload switch thus has both instantaneous switching-off and instantaneous switching-on movements whereby the contacts 7 l2 and 13 are protected.

On the overload switch becoming overheated or in the event of overload in the circuit of the two contacts 12 and 13 the bimetal strip 18 is heated and sags downwardly with respect to its position in FIG. 1 to engage the slide 32 at a stop 69 and displaces it downwardly against the holding force of the magnet limbs whereby triggering is initiated as described before.

The few moving parts of the switching lock arranged in the metal frame 9 are small and light, so that an extremely small mechanical action time of the overload switch is achieved.

If, instead of a DC current, an AC current source is connected to the connection 60, then the same conditions as already described hereinabove are produced in the first positive half-wave. In the negative half-wave, the direction of the magnetic flux 68 is reversed. In principle, this does not effect a change in the above described operation since again the holding force is always weakened for one magnet armature 55 and not greatly amplified for the other in each case. In the case of AC current, for example, 50 or 60 cycles, the same release is achieved as in the case of DC current. Due to the manner of conducting the magnetic flux, the demagnetization of the permanent magnet 44 is avoided to a considerable extent.

In the figures, the overload switch is shown substantially to a scale of 2:1. It may also be designed to be smaller, so as to be able to manufacture the moving parts as small and as light as possible.

Switches according to the invention may be triggered at extremely low energy inputs, for example of the order of 0.1 milliwatts.

In FIG. 5 the bimetal strip is represented in the same circuit as the contacts 12 and 13 and two armatures 55 are represented. Lifting of either armature 55 or movement of the bimetallic strip causes triggering of the switch and opening of contacts 12 and 13.

While it will be apparent that the teachings herein are well calculated to teach one skilled in the art the method of making the preferred embodiment of this invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or meaning of the subjoined claims.

I claim:

1. An overload switch comprising:

a magnetic core having two sets of limbs;

means for pre-establishing a flux in said limbs;

at last two magnet armatures, one of said armatures being associated with and holdable against one of said sets of limbs and the other of said armatures being associated with and holdable against the other of said sets of limbs;

a lever connecting said armatures and mounted for pivotal movement with respect to said limbs;

a pair of closable contacts;

a member carrying one of said contacts coactive with and movable by said lever to and from a position in which said contacts are closed;

spring means associated with said lever for urging said lever in a manner to move said armatures away from said limbs; and

winding means for said limbs for establishing a magnetic flux in response to current flowing in said windings which is opposite in direction in one of said sets of limbs to the direction of said pre-established flux and is in the same direction in the other of said set of limbs as the direction of said pre-established flux;

said spring urging said armatures from said limb in response to a power input to said windings above a predetermined value to move said contact from the closed position by pivoting of said lever and movement of said contact carrying member.

2. A switch as claimed in claim 1 wherein each set includes two limbs, the limbs in each said set having opposite magnetic poles adjacent said armatures.

3. A switch as claimed in claim 1 further comprising winding means for each said limb.

-4. A switch as claimed in claim 1, wherein said magnetic core is substantially magnetically saturated by said preestablished flux.

5. A switch as claimed in claim 1 wherein said means for pre-establishing a flux in said limbs is a permanent magnet.

6. A switch as claimed in claim 5 wherein said permanent magnet is cylindrical and is diametrically magnetized, and wherein said means for pre-establishing a flux in said limbs further includes two yokes bearing against said permanent magnet and said limbs.

7. A switch as claimed in claim 1 further comprising a nonmagnetic plate having a plurality of bent over portions and wherein said limbs are secured to said bent over portion of said plate adjacent ends of said limbs magnetically opposite said ends adjacent said armature and still further comprising a rotatable soft magnetic plate, said opposite ends of said limbs abutting said soft magnetic plate.

8. A switch as claimed in claim 7 further comprising an interior housing of insulating material including a wall, and means defining a hollow rivet through said wall supporting said magnetically soft plate, said non-magnetic plate, and said means pre-establishing a flux through said limbs; said latter means being located between said wall and said non-magnetic plate, and saidwindings, said lever and said armatures and said adjacent ends of said limbs being located within said interior housing.

9. A switch as claimed in claim 8 further comprising housing means for said switch and fastening means for said housing adapted to adjust the position of said magnetically soft place, said non-magnetic plate, said means pre-establishing a flux in said limbs, and said interior housing.

10. A switch as claimed in claim 1, further comprising a slide member, said lever being pivotally mounted on said slide member, andsaid spring means being effective to urge said slide member to move said lever away from said magnet core.

1 1. A switch as claimed in claim 9 further comprising a slide member, said lever being pivotally mounted on said slide member, and said spring means being effective to urge said slide member to move said lever away from said magnetic core, and an adjusting sleeve movable in said hollow rivet disposed between and abutting said spring means and said slide member.

12. A switch as claimed in claim 10 further comprising a pivotable catch member for said contact carrying member, said catch member being connected to said slide member to rotate on longitudinal movement thereof, means defining a first crank slot in said catch member having first and second parts, a support in said housing, means defining a second slot in said support, a projection on said contact carrying member,

said projection being movable in said first part of said first slot and in said second slot when said first part and said second slot are aligned, and said projection being lockable against sliding by rotation of said catch member to engage said projection in said second part of said first slot, said contact carrying member being rotatable to said contact closed position when said projection is locked.

13. A switch as claimed in claim 12 further comprising a second spring means adapted to urge rotation of said contact carrying member to said contact closed position when said projection is locked, and to urge said contact carrying member from said contact closed position when said first part of said first slot and said second slot are aligned.

14. A switch as claimed in claim 13 further comprising a fixed abutment against which said second spring means urges said contact carrying member and about which said contact carrying member is pivotable when said second part of said first slot and said second slot are aligned.

15. A switch as claimed in claim 12 further comprising a pushbutton operable to move said contact carrying member against said second spring means with said projection in said first part of said first slot, fingers on said pushbutton and said contact carrying member respectively, said fingers being engageable to prevent rotation of said contact carrying member when said pushbutton is operated, and third spring means adapted to oppose operation of said pushbutton.

16. A switch as claimed in claim 15 further comprising abutments on said contact carrying member andsaid catch, said abutments engaging during such movement of said projection on said contact carrying member in said first part of said first slot to rotate said catch.

17. A switch as claimed in claim 12 further comprising a birnetal strip and a heating coil associated with said birnetal strip, said core being electrically connected to said contact, said strip engaging said slide member and being operable on bending due to heating above a given temperature to rotate said catch by movement of said slide member to unlock said projection on said contact carrying member. 

1. An overload switch comprising: a magnetic core having two sets of limbs; means for pre-establishing a flux in said limbs; at last two magnet armatures, one of said armatures being associated with and holdable against one of said sets of limbs and the other of said armatures being associated with and holdable against the other of said sets of limbs; a lever connecting said armatures and mounted for pivotal movement with respect to said limbs; a pair of closable contacts; a member carrying one of said contacts coactive with and movable by said lever to and from a position in which said contacts are closed; spring means associated with said lever for urging said lever in a manner to move said armatures away from said limbs; and winding means for said limbs for establishing a magnetic flux in response to current flowing in said windings which is opposite in direction in one of said sets of limbs to the direction of said pre-established flux and is in the same direction in the other of said set of limbs as the direction of said preestablished flux; said spring urging said armatures from said limb in response to a power input to said windings above a predetermined value to move said contact from the closed position by pivoting of said lever and movement of said contact carrying member.
 2. A switch as claimed in claim 1 wherein each set includes two limbs, the limbs in each said set having opposite magnetic poles adjacent said armatures.
 3. A switch as claimed in claim 1 further comprising winding means for each said limb.
 4. A switch as claimed in claim 1, wherein said magnetic core is substantially magnetically saturated by said pre-established flux.
 5. A switch as claimed in claim 1 wherein said means for pre-establishing a flux in said limbs is a permanent magnet.
 6. A switch as claimed in claim 5 wherein said permanent magnet is cylindrical and is diametrically magnetized, and wherein said means for pre-establishing a flux in said limbs further includes two yokes bearing against said permanent magnet and said limbs.
 7. A switch as claimed in claim 1 further comprising a non-magnetic plate having a plurality of bent over portions and wherein said limbs are secured to said bent over portion of said plate adjacent ends of said limbs magnetically opposite said ends adjacent said armature and still further comprising a rotatable soft magnetic plate, said opposite ends of said limbs abutting said soft magnetic plate.
 8. A switch as claimed in claim 7 further comprising an interior housing of insulating material including a wall, and means defining a hollow rivet through said wall supporting said magnetically soft plate, said non-magnetic plate, and said means pre-establishing a flux through said limbs; said latter means being located between said wall and said non-magnetic plate, and said windings, said lever and said armatures and said Adjacent ends of said limbs being located within said interior housing.
 9. A switch as claimed in claim 8 further comprising housing means for said switch and fastening means for said housing adapted to adjust the position of said magnetically soft place, said non-magnetic plate, said means pre-establishing a flux in said limbs, and said interior housing.
 10. A switch as claimed in claim 1, further comprising a slide member, said lever being pivotally mounted on said slide member, and said spring means being effective to urge said slide member to move said lever away from said magnet core.
 11. A switch as claimed in claim 9 further comprising a slide member, said lever being pivotally mounted on said slide member, and said spring means being effective to urge said slide member to move said lever away from said magnetic core, and an adjusting sleeve movable in said hollow rivet disposed between and abutting said spring means and said slide member.
 12. A switch as claimed in claim 10 further comprising a pivotable catch member for said contact carrying member, said catch member being connected to said slide member to rotate on longitudinal movement thereof, means defining a first crank slot in said catch member having first and second parts, a support in said housing, means defining a second slot in said support, a projection on said contact carrying member, said projection being movable in said first part of said first slot and in said second slot when said first part and said second slot are aligned, and said projection being lockable against sliding by rotation of said catch member to engage said projection in said second part of said first slot, said contact carrying member being rotatable to said contact closed position when said projection is locked.
 13. A switch as claimed in claim 12 further comprising a second spring means adapted to urge rotation of said contact carrying member to said contact closed position when said projection is locked, and to urge said contact carrying member from said contact closed position when said first part of said first slot and said second slot are aligned.
 14. A switch as claimed in claim 13 further comprising a fixed abutment against which said second spring means urges said contact carrying member and about which said contact carrying member is pivotable when said second part of said first slot and said second slot are aligned.
 15. A switch as claimed in claim 12 further comprising a pushbutton operable to move said contact carrying member against said second spring means with said projection in said first part of said first slot, fingers on said pushbutton and said contact carrying member respectively, said fingers being engageable to prevent rotation of said contact carrying member when said pushbutton is operated, and third spring means adapted to oppose operation of said pushbutton.
 16. A switch as claimed in claim 15 further comprising abutments on said contact carrying member and said catch, said abutments engaging during such movement of said projection on said contact carrying member in said first part of said first slot to rotate said catch.
 17. A switch as claimed in claim 12 further comprising a bimetal strip and a heating coil associated with said bimetal strip, said core being electrically connected to said contact, said strip engaging said slide member and being operable on bending due to heating above a given temperature to rotate said catch by movement of said slide member to unlock said projection on said contact carrying member. 